Some filter elements include a perforated rigid support core surrounded by tubular or cylindrical fibrous filter media. Imperforate rigid plastic or metal end caps are typically located at opposite ends of the filter media, and at least one of the end caps has a central opening to allow fluid to flow into or out of the inner cavity of the filter element. The filter element can be located in a filter housing, with the element locators (fluid passages) in the housing received in the opening(s) in the end caps. In some instances, the filter media is pleated, that is, the filter media is formed with longitudinally-extending pleats extending from end cap to end cap. The pleats provide for a larger surface area in contact with fluid to be filtered, and hence increase the particle separation efficiency of the filter element. Fluid to be filtered either passes radially inward through the filter media and then outwardly through the opening in the end cap, or inwardly through the opening in the end cap and then radially outward through the filter media.
The support core for the filter element generally provides support for the pleated filter media, although certain filter media structures have been developed whereby the filter material is of such a rigidity that it is self-supporting. Self-supporting filter elements can require relatively thick media layers, epoxy-coated steel mesh layers, deep grooves in the exterior surface to increase the surface area, shallow pleat configurations, and/or a high resin content, all of which can increase the complexity, time, and cost associated with manufacturing the filter element. Self-supporting filter elements are therefor not appropriate for all filter applications. As such, many applications require a central support core for support of the filter media.
Applicants believe that filter elements with a central support core have typically been manufactured with the core formed integrally with the housing, that is, with the core fixedly attached to the surrounding filter media, such as by attachment to the opposing end caps (see, e.g., U.S. Pat. No. 4,033,881). As such, when the filter element becomes clogged or spent, the entire element, with support core, must be removed and replaced. Many fibrous filter elements are not designed to be cleaned and reused, and as such, must be disposed of in an appropriate location, such as in a landfill. The support core is not easily removed from the filter media, and as such, the core is disposed of at the same time. These two components (filter media and core) take up valuable space in landfills. Additional disposal issues can be raised when the support core is formed from a noncombustible material, such as metal, which can require the use of expensive compacting machinery for proper disposal. Moreover, the replacement filter element has costs (labor and material) associated with both the fresh filter media and the support core, particularly if the core is metal.
Certain filter elements have been developed in an attempt to separate (remove) the spent filter media from the support core when the filter media is replaced. These "green" filter elements include, for example, Mills, U.S. Pat. No. 5,476,585, which shows a permanent metal support core in the housing surrounded by a removable pleated filter element. A spiral wrap is disposed around the exterior surface of the filter media to provide resistance against axially-directed forces. End cap portions on the filter media and on the core are fluidly sealed together and can be separated to remove the spent filter media from the core. Tokar, et al., U.S. Pat. No. 4,211,543 also shows a pleated filter media having an outer liner supporting the outer pleat peaks of the media. This reference also discloses that the filter media can be slid onto a conically-shaped safety sleeve assembly, which has been initially located over a rigid support core. Kott et al., U.S. Pat. No. 5,211,846, discloses to provide circumferential straps around the exterior of the coreless filter element to maintain the cylindrical shape of the filter media and to maintain separation of the pleats. On the other hand, Gewiss et al., U.S. Pat. No. 5,413,712 discloses to locate pleated (zig-zag) filter media directly over a rigid support core with no external wrap.
While the Mills, Tokar, Kott and Gewiss patents appear to allow the filter media to be removed from a support core permanently affixed the filter housing, it is believed that the filter media can be difficult to locate over the core, particularly if the filter media is pleated because the inner peaks of the pleats can become distended or bent when the filter element is closely received over the support core. Further, the pleated filter media requires some structure to hold the pleats in fixed, closely-held relation with one another such that "lay-over", i.e., the folding over of the pleats against one another, is prevented. While the Mills, Tokar and Kott patents teach to provide an exterior wrap around the pleats, wrapping the exterior surface, particularly with a helical or spiral wrap, can be time-consuming and require significant amounts of wrap material. An exterior wrap can also have issues with appearance. The Gewiss patent, on the other hand, does not provide an outer wrap, and so can be unacceptable for many applications where a significant pressure drop across the element is expected.
As such, it is believed that the prior known designs for filter elements have not provided a coreless filter element which can be simply and easily located over a support core in the housing and removed from the housing when spent and replaced, which has a filter media structure which maintains the structural integrity of the pleats during use, and which is relatively simple and cost-effective to manufacture. Moreover, it is believed that there is a demand in the industry for a coreless filter element which does not have an outer wrap around the pleats, does not incorporate the drawbacks associated with many of the "self-supporting" types of filter elements, and which can be easily disposed of in landfills.